Process for producing oxygen



Feb. 26, 1952 P. w. @ARBO PROCESS FOR PRODUCING OXYGEN 2 SHEETS--SHEET l Filed Nov. l, 1947 INVENTOR. Paul fia/'d BY frm/mfr Feb. 26, 1952 P. w. GARBo PROCESS FOR PRODUCING OXYGEN Filed Nov. 1, 1947 2 SHEETS-SHEET 2 w. d. f@ f W@ \%b NN vPatented Feb. 26, 1952 PROCESS FOR PRODUCING OXYGEN Paul W. Garbo, Freeport, N. Y., assignor to Hydrocarbon Research Inc.,

corporation of New New York, N. Y., a

Application November 1, 1947, Serial No. 783,551

19 Claims. (Cl. 62-175.5)

This invention relates to the production of oxygen by the liquefraction and rectification of air, and more particularly to an economical method of obtaining oxygen in high purity and in high yield Without the use of chemical reagents to effect the removal of carbon dioxide present in air.

All temperatures herein are in degrees F. and pressures in pounds per square inch gauge.

Oxygen is commonly produced by liquefaction of air and rectification at low temperatures; preferably rectification is conducted in two stages at different pressures. The refrigeration necessary for liquefaction is supplied to the air, after it has been compressed and Water-cooled to approximately room temperature, by indirect heat ex'- change with the effluent products of rectification. However, an additional amount of refrigeration must be supplied to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectiiication and for heat leaks into the system. Methods of supplying this refrigeration heretofore used involve compressing at least a portion of incoming air to pressures as high as 3000 pounds and expanding with or without the performance of work to produce a temperature drop; or compressing all the incoming air to about 600 pounds and after the air has been partially cooled by the products of rectification expanding a portion of the air. These methods are wasteful from the standpoint of compressor energy and require a great deal of equipment in the form of extra compressors, intercoolers and expanders.

For economical operation it is essential to recover the cold content of the outgoing products of rectification. This is usually accomplished by passing these products in heat transfer relationship with the incoming air. In older systems, in order to avoid deposition of frost and solid carbon dioxide in the tubular countercurrent heat exchangers through which the air is passed in indirect heat exchange relation with the outgoing products of rectification, the air is treated in driers and caustic scrubbers to remove water and carbon dioxide prior to admittance of the air into the heat exchangers. Even with this treatment the exchangers had to be thawed out regularly to remove the frost which term is used in a generic sense to include both snow and ice) which caused stopping up of the apparatus.

More recently it has been suggested to use cold accumulators or regenerators (hereinafter referred to as heat exchangers) ci large cold absorbing capacity through which the warm incoming air and the cold products of rectification are alternately passed with periodically reversed operation so that streams of warm air are iiowed through the same packing-filled spaces that the cold separated oxygen and nitrogen traversed during the previous step in the process, the high boiling impurities deposited in these spaces during the passage of air therethrough being removed by sublimation during the subsequent fiow in a reverse direction of the products of rectification. The use of these reversing heat exchangers in a process in which the air is compressed to relatively high pressure results in more costly operation from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heat exchangers is lost and must be again replaced. Moreover, in the operation of such reversing heat exchangers it is important not to let the temperature at the exit end of the exchangers drop to a point where a part of the air becomes liquid because this liquid adheres to the surface of the exchangers and is wasted upon reversal of flow.

Among the objects of this invention are to provide a process of vproducing oxygen by the liquefaction and rectification of air, in which the carbon dioxide and preferably also the moisture are removed from the air without the use of chemical reagents by fiow through reversing heat exchangers of the regenerator or recuperator type, operated at relatively low pressures, of the order of about to 100 pounds, so that the loss of compressed air in the exchangers upon each reversal is small; and the reversing exchangers are operated under conditions such that the carbon dioxide deposited therein is removed efliciently to permit substantially continuous operation of the process and notwithstanding the use of a rectification product stream to improve the efilciency of the carbon dioxide purging a portion of this rectification product stream may be Withdrawn in substantially uncontaminated condition, i. e., not contaminated with condensible constituents removed from the air stream.

Other objects and advantages of this invention will be apparent from the following detailed description.

In accordance with this invention, a stream of rectification product is passed through a path in a heat exchange zone and a stream of air is passed through another path in this heat exchange zone. The air is thus cooled to a temperature close to its condensation point at the 3 pressure existing in the heat exchange zone thereby substantially completely removing all carbon dioxide present in the air. The iiow of these two streams is periodically reversed so that the air iiows through the path through which had previously flowed the rectication product and the rectification product lflows through the path through which had previously flowed the air, the rectification product effecting the removal of carbon dioxide deposited in the heat exchange zone during the preceding step of the process. A non-reversing stream of rectification product preferably oxygen is passed through at least the cold end of the heat exchange zone where deposition of carbon dioxide takes place in indirect heat exchange relation with the air and the first mentioned stream of rectification product; this non-reversing stream of rectification product is thus warmed. A portion of this non-reversing stream of rectification product is withdrawn as product uncontaminated by carbon dioxide or other condensible constituents deposited in the heat exchange zone from the air stream passing therethrough. The remainder of this stream of rectification product is recirculated through its flow path in the heat exchange zone, augmented by additional rectification product from the rectification system.

By circulating a rectification product stream through a fixed path in at least the cold end of the heat exchange zone, the temperature conditions within this cold end are maintained such that efficient purging of this heat exchange zone takes place during each reversal period. Further, since the non-reversing rectification product stream flows through a fixed path through which the air never passes, efficient purging is effected without contaminating the non-reversing rectification product stream with air.

More specifically, in accordance with this invention a stream of air at about 60 to 100 pounds and at a temperature of about 70 to about 110 F. is passed through a heat exchange zone in heat exchange relation with a stream of nitrogen rectification product or oxygen rectification product or both nitrogen and oxygen rectification products and the iiow of the air stream and the rectification product stream or streams periodically reversed so that the rectification product or products fiow through the path through which had previously flowed the air and thereby effect removal of carbon dioxide deposited in the heat exchange zone during the preceding step of the process. In addition, a non-reversing stream of rectification product, preferably oxygen, is passed through at least the cold end of the heat exchange zone where deposition of carbon dioxide takes place in indirect heat exchange relation with the air and the other stream or streams of rectification product or products; this non-reversing stream of rectification product is thus warmed. A portion of this non-reversing stream of rectification product is Withdrawn as product uncontaminated by carbon dioxide or other condensible constituents deposited in the heat exchange zone from the air stream passing therethrough. The remainder of this stream of rectification product is recirculated through its iiow path in the heat exchange zone augmented by additional rectification product from the rectification system.

The. stream of air leaves the heat exchange zone at a temperature below about 270 F. but above its condensation point. This stream is divided into two streams, one comprising the The non-reversing rectification product stream also desirably flows in heat exchange relation with a reversing rectification product stream, preferably nitrogen, to heat this stream to a temperature within 5 to 10 F., preferably 6 to 8 F., below the temperature of the exiting air stream, thereby conditioning the reversing rectification product stream so that it effects more eflicient removal of carbon dioxide deposited in the exchanger during the preceding step of the process. The minor portion of the air stream which is warmed is then expanded to produce the refrigeration necessary to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system. The expanded air is introduced into the low pressure stage of the rectification system where its oxygen content is recovered. The low pressure stage is generally operated under a pressure of from about 5 to 12 pounds, preferably at about 7 to 9 pounds; the high pressure stage is maintained at a pressure of from about to 100 pounds, preferably at about 75 to about pounds. The remaining major portion of the air is also introduced into the rectification system where it is rectified to recover its oxygen content.

Thus when operating in accordance with this invention, the minor portion of the air which is to be expanded is first cooled to a temperature such as to eect the complete removal of carbon dioxide therefrom, permitting operation of the expander without encountering the troubles heretofore experienced because carbon dioxide solidified in the expander during the expansion of the air stream. The warming of the air stream before expansion to a temperature such that upon subsequent expansion little or no condensation or formation of liquid air in the expander takes place results in a further improvement in the operation of the expander. 'I'he warming of the reversing rectification product stream prior to its introduction into the heat exchange zone to a temperature within 5 to 10 F., preferably 6 to 8 F., of the exiting air stream results in satisfactory purging of the fiow path through which this rectification product stream passes. Since the non-reversing rectification product stream flows through a fiow path in the heat exchange zone through which the air never passes, it is not contaminated by carbon dioxide and other condensibles removed from the air, and, hence, provides a relatively pure rectification product and at the same time efficiently supplies the heat necessary for warming (l) the air stream prior to its expansion to obtain the above noted improvements in the expander, and also (2) the reversing rectification product stream to obtain the above noted efficient periodic purging of the heat exchange zone.

In the accompanying drawings forming a part of this specification and showing, for purposes of exempliiication, preferred layouts of equipment for practicing the process of this invention,

Figure 1 illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention; the apparatus of this figure involves heat exchangers of the recuperator type;

Figure 2 illustrates a modified arrangement of heat exchangers of the regenerator type which may be used in lieu of the exchangers of the recuperator type shown in Figure 1;

Figure 3 illustrates still another modified arrangement of exchangers of the regenerator type;

and

Figure 4 illustrates still another modified arrangement of apparatus involving exchangers of the recuperator type for practicing the process of this invention.

It will be understood the drawings illustrate diagrammatically preferred apparatus for practicing this invention and that the invention may be carried out in other apparatus. For example, any desired number of reversing exchangers of either the recuperator or regenerator type may be used in lieu of the reversing exchangers shown in the drawings; each of the reversing exchangers of the drawings may be replaced by two or more similar exchangers placed in series and/ or parallel, if desired; the divided or split exchangers hereinafter described may be disposed in a single housing or may be constructed as separate and distinct units; other rectification systems may be used in lieu of those shown in Figures l and 4 including rectification systems equipped with means for purging the high pressure stage to remove incondensible gases, such as helium, hydrogen and neon therefrom, or the rectification system of Figure 4 may be used with the exchangers of Figures 1, 2 and 3, or that of Figure l may be used with the exchangers of Figures 2, 3 and 4; the manner of providing refrigeration to compensate forrcold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system disclosed'in Figure 1 may be employed with the exchangers shown in the other figures of the drawings, or conversely the manner of providing such refrigeration shown in Figure 4 may be used with the exchangers of the other figures of the drawings.

In the drawings, in which like reference characters indicate like parts, referring to Figure 1, Ill is a heat exchanger which may be of any well known type. In the embodiment shown in Figure l it consists of two sections I0a and Ib. Section Ia is provided with three flow paths, namely, interior path II and concentric paths I2 and I3 disposed in heat exchange relation with each other. The heat exchanger has in each of the paths suitable fins of heat conducting material, e. g., copper or aluminum, for promoting rapid and efficient heat exchange between the gaseous media flowing therethrough4 For purposes of illustration and in the interests of simplicity each fiow path in an exchanger is shown on the draw- -f ings as being formed of a single tube, the several pathsA being. disposed concentrically. Actually, however, each path in each exchanger may comprise a multiplicity of tubes for flow therethrough. One form of the exchanger of the recuperator type, shown diagrammatically in Figures 1 and 4, which may be used in practicing the process of this invention is disclosed and claimed in application Serial No. 676,142, filed June l2, 1946. As the construction of the heat exchanger per se does not form a part of this invention and as it may be of any well known type, it is believed further description thereof is unnecessary.

Exchanger section Illb has three fiow paths I5,

I6 and I'I. Flow path I1 is connected with path I3 by line I8 and flow path I6 is connected with path I2 by line I9. Flow path I5 communicates with flow path II through a line provided with a branch line 2I, the function of which will be hereinafter described.

Paths I2 and I3 of section Illa and I6 and I1 of section Ib are the paths through which air and nitrogen flow, the flows of these two media through their respective paths being periodically reversed so that during one step of the process air flows through paths I2 and I6 and nitrogen fiows through paths I'I and I3 and upon reversal during the succeeding step air flows through paths I3 and I'I and nitrogen through paths I6 and I2. Reversal of fiow is accomplished by suitably positioning compound reversing valves 22, 23 which may be of any well known type. Valve 22 is disposed in a pipe line system consisting of (a) air inlet pipe 24 leading into valve 22, (b) nitrogen exit line 25 leading to any suitable point of nitrogen disposal, and (c) lines 26 Aand 2l' communicating with paths I2 and I3, respectively, as shown in Figure 1. Lines 28 and 29 lead from the .iiow paths I6 and I'I to valve 23` Nitrogen inlet line 33 leads into valve 23, and this valve is provided with an air exit line 3 I.

Flow path I5 is provided with an oxygen inlet line 32, the oxygen fiows through path I5, thence into line 20; a portion is withdrawn through branch line 2l and the remainder passes through ow path II into an oxygen exit line 33. No reversal of flow of the oxygen relative to the gaseous streams passing through the exchanger I0 takes place.

rl`he rectification system of Figure l comprises a two-stage rectification column 34, the lower section 35 of which is operated at a pressure of about 60 pounds to about 100 pounds, preferably about 75 to 90 pounds, and the upper section 36 of which is operated at a pressure of from about v5 pounds to about 12 pounds, preferably at about 7 to 9 pounds. This column, as is customary, is provided with rectification plates of the bubble cap or other desired type. The lower section 35 communicates with a condenser 3i and has a liquid collecting shelf 38 disposed immediately below the condenser for collecting liquid nitrogen. Pipe line 39 leads from shelf 38 to a non-reversing heat exchanger 40 which communicates through a pressure reducing valve 4I with the top portion of the low pressure stage 36. Condenser 37 acts as a reboiler for the upper section 36.

From the base of the lower section 35 a pipe line 42 for the flow of crude oxygen passes to a non-reversing heat exchanger 43 which communicates through pipe line 44 having a pressure reducing valve 45 therein with the low pressure section 36 at an intermediate point 46. A line 41 having a pressure reducing valve 48 therein leads from condenser 31 to a nitrogen line 49. A line leads from the top of the low pressure section 36, passes through heat exchangers 40 and 43 and enters line 49; the nitrogen stream iiowing through line 50 enters line 49 where it joins the stream from line 41. Nitrogen line 45 enters a non-reversing heat exchanger 5I which has a nitrogen exit line 52 leading into a nonreversing heat exchanger 53 provided with a nitrogen exit line 54 communicating with line 3l entering valve 23. A by-pass line 55 provided with a valve 55 therein by-passes the exchanger 53 so that more or less of the nitrogen flowing through line 52 and depending upon the position of valve 55 maybe caused to by-pass the heat exchanger 53, thereby controlling the temperature of the nitrogen entering the valve 23.

1An oxygen line 51 leads from the low pressure section 35 to line 32 which leads inw flow path I of section IIIb.

Branch line 2| communicates with a pump or blower 60 for pumping the oxygen fiowing through branch 2| through a line 6| leading into a nonreversingexchanger 62. From the non-reversing exchanger 62 a line 63 leads into and through the non-reversing exchanger 53, line 63 communicating with the oxygen line 32 at 64.

Air line 3| is provided with a branch 65 having a valve 66 therein which leads into and through the exchanger 62, thence through line 61 into an expander 68 from which a line 68 leads into the low pressure section 36 of rectification column 34. A by-pass line having a valve 1I therein extends from the airline 3| to line 61 leading into the expander 68. More or less of the air entering the expander 68 depending upon the setting of the valves 66 and 1I may thus -be by-passed about the exchanger 62, thereby controlling the temperature of the air entering the expander 68. Air line 3| extends through the non-reversing heat exchanger 5I and enters the high pressure stage of the rectification column 34 at 12.

In operation of the equipment of Figure 1. air from the main air line 24 flows through valve 22, line 26, path I2, line I8, path I6, line 28, valve 23, line 3|. In its flow through path I2 the air is cooled to a temperature sufficient to remove all moisture, if any, present in the air. In its flow through path I6 the air is cooled to a temperature near its condensation point, so that all carbon dioxide is removed therefrom and deposited in the flow path I6. The major portion of the air leaving path I6 ows through line 3|, non-reversing exchanger 5| into the high pressure stage of the rectification system at 12. The remaining minor portion iiows through lines 65 and 10. that flowing through 65 passing in indirect heat exchange relation with warm oxygen flowing through exchanger 62, whereby the air is warmed. The thus warmed air mixes in line 61 with the air flowing through line 10 to produce a mixture at a desired temperature such that upon expansion no liquid air is formed in expander 68. The expanded air from expander 68 flows through line 69 and enters low pressure stage 36 of the rectification column 34.

Nitrogen iiows from the low pressure stage 36 through line 50 and a minor nitrogen stream vented from the condenser 31 in order to purge helium and other incondensible gases flows through line 41, both streams entering line 43. 'I'he resultant nitrogen stream passes through non-reversing heat exchanger 5|, into and through line 52 from which at least a portion of the nitrogen passes through the non-reversing heat exchanger 53 where it ows in heat exchange relation with the warmed oxygen stream passing through this exchanger. From this exchanger the warmed nitrogen flows through line 54 into line 30 entering valve 23. If desired, a portion oi' the nitrogen stream from line 52, the amount depending on the setting of valve 56, flows through line 55 by-passing exchanger 53 and mixes in line 30 with the warmed nitrogen which has passed through exchanger 53; thus the temperature of the nitrogen stream entering valve 23 is controlled so that the nitrogen enters at a temperature at which it will eilect emcient purging of the ow paths in exchangers IIb and Ila through which it flows. From valve 23 the nitrogen stream during one cycle flows through line 23. path I1. line I3. path I3, line 21, valve 22 into nitrogen exit line 25.

Oxygen flows through lines 51 and 32 into and through flow path I5. In its ow through this iiow path the oxygen is warmed by indirect heat transfer with the air stream flowing through the exchanger. The oxygen leaves path I5 through line 2li. A portion of the oxygen from line 2| is returned by blow through the non-reversing heat exchanger 62 where it gives up some of its heat to the air stream passing through this exchanger to warm this air stream. From exchanger 62 the oxygen flows through line 83 into and through exchanger 53 where, as above described, it gives up additional heat to the nitrogen stream flowing through this exchanger. 'I'he recirculating oxygen stream then enters oxygen line 32 mixing with the oxygen stream flowing from the rectification column 34; the resultant oxygen stream enters path I5 through line 32. The remainder of the oxygen stream not recirculated by blower 60 through the exchangers 62 and 53 flows from line 20 through path II of exchanger Ia and is withdrawn as product oxygen through the exit line 33.

Upon reversal, as indicated by the dotted setting of reversing valves 22 and 23, which reversal may take place every three minutes, air flows through line 24, 1ine 21, flow path I3, line I8, iiow path I1. line 29, valve 23 into line 3|. The major portion of the air from line 3| iiows through heat exchanger 5I into the high pressure stage 35 of the rectification column 34. The remaining minor portion flows as hereinabove described so that it is warmed by the recirculating oxygen stream passing through exchanger 62 and is thus warmed before expansion in expander 68, the expander air flowing through line 69 into the low pressure stage 36 of the rectification column 34. Nitrogen enters valve 23 through the same fiow system as hereinabove described and flows through line 28, path I6, line I9, path I2, line 26, valve 22 to the nitrogen exit line 25. Oxygen flows through line 32, path I5, a portion oi the oxygen from line 20 being recirculated by blower 68 through heat exchanger 62, line 63, heat exchanger 53, line 32, back to the iiow path I5, the remainder passing through path II to the oxygen exit line 33.

Thus, it will be noted that flow through the flow paths I5 and II always takes place in the same direction throughout the operation of the process. On the other hand, flow of the nitrogen and air through their respective iiow paths is periodically reversed, the nitrogen on each reversal flowing through the path through which had previously passed the air and removing from this path carbon dioxide and other condensibles removed from the air stream during the preceding step of the process. Since the oxygen stream employed to condition the nitrogen stream to effect more eiiicient purging flows through a path in the exchanger through which air never passes, it is not contaminated by condensibles removed from the air stream.

The exchanger system of Figure 2 differs from that of Figure 1 chiefly in that (1) the exchangers of Figure 2 are of the regenerator type and 2) the recirculating oxygen stream flows through the entire length of the exchangers, whereas in Figure 1 the recirculating oxygen stream flows through section |b only and not through section a.

In Figure 2, 15, 16 are a pair of regenerators each containing material, such as copper or aluminum, of high heat transfer capacity over which ow alternately streams of rectification product andA air, the rectification product imparting its cold content to this material and the air recovering this cold when it flows thereover during the succeeding step of the process, as is well known in this art. Extending through the regenerators 15, 16 are rxygen flow paths 11, 18, respectively. Each of these flow paths desirably is in the form of one or more tubes of high heat conducting material, such as copper or aluminum; the oxygen passing therethrough is in indirect heat exchange re'ationshipY with the material of high heat transfer capacity in the re- `generatorsA 15, 16. Path 11 is connected with oxygen line 32 by a line 19 and path 18 is connected with oxygen line 32 by a line 8|. 'I'he exit ends of these oxygen Ilow paths 11 and 18 lead into lines 83 and 84, respectively, which in turn communicate with an oxygen line 85 provided with a branch 86. As in the modification of Figure 1 a blower 60 may be disposed in the branch 88 for recirculating a portion of the oxygen owing through line 85 through non-reversing heat exchangers 62 and 53 into the oxygen line 32 where the recirculated oxygen mixes with the stream of oxygen flowing from the rectification system, the resultant oxygen stream owing through the flow paths 11 and 18.

Reversing valve 22 is provided with a line 81 leading into the regenerator and a second line 98 connecting this valve with regenerator 16. The other reversing valve 23 is provided with a pair of lines 89 and 90 connecting this valve with regenerators 15 and 16, respectively. By means of these reversing valves the ow of air is caused to take place alternately through regenerators 15, 18 and the flow of nitrogen alternately l through the regenerators 16 and 15 so that during each stem air flows through one regenerator and nitrogen through the other and upon reversal the air flows through the regenerator through which had previously flowed the nitrogen and the nitrogen flows through the regenerator through which had previously flowed the air.

In the operation of the modification of Figure 2 air at a pressure of 60 to 100 pounds and a temperature of from 70 to 110 F. supplied through line 24 flows through valve 22, line 88 into and through the regenerator 16 where it is cooled to a temperature close to its condensation point at the pressure prevailing in this regenerator. The thus cooled air exits through line 90 into valve 23 from which the air flows through line 3| to the rectification system as hereinabove described in connection with the description of Figure 1. Simultaneously, nitrogen flows through line 30, valve 23, line 89 into and through the regenerator 15 giving up its cold to the heat transfer material in regenerator 15. The thus warmed nitrogen stream exits through line 81, valve 22 and nitrogen exit line 25. Oxygen from the rectification system flows through line 32, lines 19. 8|, oxygen flow paths 11, 18, lines 83, 84 into the oxygen line 85.

mainder recirculated by blower 60 through line v minutes, as indicated by the dotted line valve set- A portion of this oxygen is withdrawn as product and the retings, air flows through valve 22, line 81 into and through the regenerator 15 and is refrigeratedv to a temperature close to its condensation point 'in its flow through this regenerator. The air exits through line 89 flowing into and through valve 23 into line 3| from which the air flows through the same lines as hereinabove described in connection with the description of Figure l. Simultaneously, nitrogen flows from line 30 through valve 23, line 90 into and through the regenerator 16, line 88, valve 22 and exits through the nitrogen exit line 25. Oxygen ows through the same paths as during the preceding step of the process; namely, through the oxygen flow paths 11 and 18 countercurrent to the stream of air flowing through one of the regenerators 15, 16 and cocurrent with the stream of nitrogen flowing through the other regenerator in indirect heat exchange relation therewith.

The nitrogen which alternately ows through one or the other of the regenerators 15 and 1B removes therefrom carbon dioxide and other condensibles deposited therein during the preceding step of the process. The eiciency of the purging action of the nitrogen is materially improved by the recirculated stream of oxygen, which stream of oxygen results in temperature conditions within the regenerators optimum for eiecting removal of carbon dioxide by the nitrogen stream flowing therethrough.

The modification of Figure 3 may be used with a rectication system such as disclosed in Figure 1 or 4. This modification differs from that of Figure 2 chiefly in four respects, i. e.,

1. Two sets of regenerators are used instead of a single set, one set being employed for the alternate iiow of oxygen and air therethrough and the other set for the alternate flow of nitrogen and air.

2. The regenerators of each set are split or divided into two sections.

3. Nitrogen rectication product instead of oxygen is recirculated through ow paths in the regenerators in indirect heat exchange relationship with the gaseous media flowing therethrough.

4. The recirculated nitrogen stream, as in the modication of Figure l, is passed through a portion only of the extent of each regenerator set, and a portion of the nitrogen is withdrawn as product uncontaminated by condensible constituents removed from the air.

In Figure 3 the two sets of regenerators are indicated by A and B. In the embodiment shown on the drawing set A comprises one regenerator consisting of sections 9 I, 92 connected by a line 93 and a second regenerator consisting of sections 94 and 95 connected by a line 98. The regenerators of set A are for alternate now of air and nitrogen therethrough. Set B comprises one regenerator consisting of sections 91, 98 connected by a line 99 and a second regenerator consisting of sections |00, |0| connected by a line |02. The regenerators of set B are for alternate ow of air and oxygen therethrough and desirably are of approximately one-fourth the volumetric capacity of the regenerators of set A. Sections 9| and 92 have nitrogen flow paths |03, |04 passing therethrough and interconnected by a line |05. Similarly sections 84 and 95 have nitrogen ilow paths |08, |01 passing therethrough and interconnected by a line |08. Section 98 has a nitrogen flow path |09 and section |0| a nitrogen vilow path |0 passing therethrough and leading into lines and ||2, respectively. Lines and ||2 communicate with a line I I3 which is also connected with lines |05 and |08. Except as above noted the regenerators of sets A and B are constructed the same as the regenerators of Figure 2.

Reversal oi' ow through the regenerators of set A is accomplished by a pair oi reversing valves ||4 and I|5. Valve ||4 is connected with regenerator section 8| by a line ||6 and with regenerator section 94 by a line ||1. Air line ||8 is provided with a branch ||9 which leads into Y valve ||4. A nitrogen exit line leads from the valve ||4. Reversing valve ||5 is connected with regenerator sections 92 and 95 by lines |2| and |22, respectively. A nitrogen line |23 leads from the rectication system into the reversing valve ||5. Air line |24 leads from reversing valve I |5 to the rectication system.

Reversal oi' now through the regenerators of set B is accomplished by a pair of reversing valves |25 and |26. Valve |25 is conected with regenerator sections 91 and |00 by lines |21 and |28. A line |29 leads from the main air line ||8 to valve |25; an oxygen exit line |30 leads from this valve. Valve |26 is connected with regenerator sections 98 and |0| by lines |3| and |32, respectively. Oxygen line |33 communicates with valve |26. Air line |24 is provided -with a branch leading from valve |26.

A branch line |35 leads from the nitrogen line |23 to the lines |36, |31, |38 and |39 communicating with nitrogen flow paths |04, |01, |09 and I|0, respectively. Nitrogen flow paths |03 and |06 are provided with nitrogenvexit lines |40 and I4| leading into a nitrogen product line |42. Line I3 which receives the nitrogen recirculated through the iiow paths |04, |01, |09 and ||0 communicates through a line |43 with branch line |35 thus completing the circulating system for the recirculated nitrogen, which system consists of the nitrogen branch line |35 connecting lines |36, |31. |38 and |39, nitrogen flow paths |04, |01, |09 and I|0, nitrogen exit lines |05, |08, and ||2, line ||3, connecting line |43 and a pump |44 in line |43 for effecting the recirculation of the nitrogen through this circulating system. Heat exchangers may be disposed in line |43 as shown in Figure 1 in connection with line 6|.

In the operation of the modification of Figure 3 air is admitted through line ||8 to valves |I4 and |25 and flows through regenerator sections 94 and |00 then through connecting lines 96, |02 into and through regenerator sections 95 and |0| into and through the lines |22 and |32 through the valves ||5 and |26 into the air line |24. Simultaneously, oxygen flows through line |33, valve |26, line |3|, regenerator section 98 through the connecting line 99 into and through regenerator section 91, line '|21 into valve |25 and exits |05 and |08, respectively, connected with line ||3. Part o! the nitrogen from line ||3 is recirculated by pump |44 through line |43 into line |35 where it mixes withthe nitrogen entering line |35 from line |23. The resultant mixed nitrogen stream, as hereinbefore described, ows through the ilow paths |04, |01, |09 and ||0. The remainder of the nitrogen in line ||3 iiows through lines |05 and |08 and ilow paths |03 and |06 in the regenerator sections 9| and 94 and exits from these flow paths through lines |40 and |4| entering the nitrogen exit line |42 from which the nitrogen uncontaminated with condensibles removed from the air stream is withdrawn as product.

The relative proportions oi' nitrogen flowing through regenerators A and that flowing through the ilow paths within these regenerators may be varied as desired. For example, from 70% to by volume of the nitrogen rectification product may be passed through regenerator A to effect purging and the rest passed through the flow paths.

Upon reversal, which may take place every three minutes, as indicated by the dotted line valve settings, air ilows through regenerator sections 9| and 91, thence through the regenerator sections 92 and 98, through the communicating lines |2| and |3| into and through valves ||5 and |28 and into the air line |24. Simultaneously, oxygen flows from hne |33, through valve |28, line |32, regenerator section |0I. line |02, regenerator section |00, line |28, valve |25. into and through the oxygen exit line |30. The oxygen in its ilow through'the regenerator sections |00 and |0| removes therefrom carbon dioxide and other condensibles deposited therein by the air in its ilow through these regenerator sections during the preceding step of the process. Nitrogen ilows from line |23 through valve I5, line |22 and regenerator sections 95 and 94, line H1, valve ||4 into nitrogen exit line |20. This nitrogen stream removes from regenerator sections and 94 carbon dioxide, frost and other condensibles deposited therein by the air stream owing therethrough during the preceding step of the process. Nitrogen also ilows through line |35, connecting lines |36, |31,|38 and |39 inw the nitrogen flow paths |04, |01, |09 and ||0 and thence through lines |05, |08, and ||2, respectively in' line ||3. As hereinabove described, a portion of the nitrogen in line ||3 is recirculated by pumpv or blower |44 through the nitrogen ow paths and the remainder iiows through lines |05 and |08, through the flow Paths |03 and |06 in regenerator sections 9| and 94' into the nitrogen exit lines |40 and |4| leading into line |42 from which the nitrogen rectiilcation product is withdrawn uncontaminated by carbon dioxide and other condensibles removed from the air stream passing through these regenerators.

The nitrogen flowing through line ||3 to the line |35 may, if desired, be passed in heat exchange relationship with a minor portion of the air stream withdrawn from line |24 to supply heat to this minor portion of the air stream prior to expanding same in a manner corresponding to the ow of the recirculating stream passing through exchanger 82 in the modification of Figure l. Alternatively, the recirculating nitrogen stream may pass through a refrigeration system, as hereinafter described in connection with the modification of Figure 4, refrigeration being supplied thereto in amount adequate to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system. The regenerator system of Figure 3 may be operated with a portion of the oxygen rectification product stream recirculated, as shown with the recuperators of Figure 4, through the flow paths in the exchangers instead ofrecirculating a portion of the nitrogen rectification product, as hereinabove described.

The modification of Figure 4 differs from that of Figure 1 chiefly in that (1) two sets of exchangers of the recuperator type, one for the reversal of air and nitrogen and the other for the reversal of air and oxygen are used;

(2) refrigeration to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system is supplied by a refrigeration system and not by expanding a minor portion of the air, as in the modification lof Figure 1; and

(3) a. two-column rectification system is used in lieu of the unitary column shown in Figure l.

In Figure 4 reference characters C and D indicate two sets of heat exchangers of the recuperator type; C is the heat exchanger in which iiow of air and nitrogen is reversed, and D is the exchanger in which the iow of air and oxygen is reversed. In general these exchangers are of substantially the same design and construction as the exchanger I of Figure 1. Exchanger D is of approximately one-fourth the volumetric capacity of exchanger C. The latter exchanger comprises two sections, |48, |49; section |48 consists of two fiow paths |50 and |5| connected by lines |52 and |53 with the flow paths |54 and |55 of the section |49. Section |49 comprises a third ow path |56 for the flow of oxygen therethrough. Exchanger D comprises two sections |51 and |56. Section |51 is provided with three flow paths |59, |60 and |6| and section |58 is also provided with three flow paths |62, |63 and |64. Flow paths |59 and |62 are connected by a line |65; ow paths |60 and |63 are connected by a line |66 and flow paths |6| and |64 are connected by a line |61.

Reversal of flow through exchanger C is effected by a pair of reversing valves |68 and |69. Valve |66 is connected with flow paths |50 and |5| by lines |10 and |1|. Air line' |12 has one branch |13 leading into valve |68 and this valve is provided with a nitrogen exit line |14. Valve |69 is connected with fiow paths |54 and |55 by lines |15 and |16. Valve |69 has a nitrogen line |11 leading thereinto and is provided with an air exit line |18.

Reversal of flow through the exchanger D is effected by a pair of reversing valves |19 and |60. Valve |19 is connected with flow paths |59 and |60 by means of lines |6| and |82. Valve |19 has a branch line |83 leading thereinto from the air line |12. This valve is also provided with an oxygen discharge line |84. Valve |80 is connected with iiow paths |62 and |63 by lines |65 and |86. This valve has leading therefrom an air line |61; an oxygen supply line |88 leads into this valve.

The rectification system comprises two columns 200 and 20|. Column 200 is operated at a pressure of from about 60 pounds to about 14 100 pounds, preferably at about 75 pounds to 90 pounds, and column 20| at a pressure of from about 5 pounds to about 12 pounds, preferably at about 7 to 9 pounds. These columns, as cus- 5 tomary, are provided with rectification plates of the bubble-cap or other desired type. Air is supplied to the base portion of the high pressure column 200 through an air line 202 into which lead the lines `|18 and |61, and which lo passes through non-reversing heat exchangers 203 and 204 hereinafter more fully described. ACrude oxygen containing approximately 40% oxygen, the rest being chiefly nitrogen, flows from the base of column 200 through line 205 l5 which passes through a non-reversing heat ex- 'changer 206. Upon now through an expansion valve 201 in line 205 crude oxygen is ashed entering column 20| at 206. Line 209 leads from the top of column 200. passes through a non- 20 reversing heat exchanger 2|0 into a line having one branch 2|| for returning liquid reflux comprising chiefly nitrogen to column 200, and another branch 2|2 passing through a non-reversing heat exchanger 2|3 and leading into the low pressure column 20| at 2|4. An expansion valve 2|5 is disposed in the branch 2|2.

The base of column 20| is provided with a line 2|6 passing through the non-reversing heat exchanger 2|0, this line having a return p0rtion 2|1 leading into the low pressure column 20| at its base. The lines 2|6 and 2I1 and the cooperating heat exchanger 2|0 function as a reboiler; liquid oxygen flows through line 2|6 through exchanger 2|0 in indirect heat exchange 'i5 relation with the gaseous stream comprising chiefly nitrogen passing through line 209 which causes vaporization of the liquid oxygen to take place, the oxygen vapors flowing into column 20| through line 2|1. A nitrogen line 2|6 leads 40 from the top of column 20|, passes through exchangers 2|3, 206, 204 and 2|9 and communicates with line |11 leading to the reversing valve |69. An oxygen line 220 leads from the base lof column 20|, passes through the exchanger 203 and communicates with the oxygen line |68 leading to the reversing valve |80.

Oxygen ow path |56 is provided with an exit line 22| leading into a line 222 which communicates with line |61 connecting oxygen flow paths |64 and |6|. A pump 223 is disposed in line 222. This line passes through a refrigeration system 224, which may be of any well known construction for supplying a refrigerating medium, such as ethylene or methane to cool the recirculating oxygen stream flowing therethrough. This refrigerating system operates to cause the iiow of the refrigerating medium in indirect heat exchange relation with the oxygen, the rate of flow and the temperature of the 30 various media being so controlled that enough cold is introduced by refrigeration at this point in the process to compensate for cold losses resulting from the difference in enthalpy between -the incoming air and the outgoing products of 65 rectification and for heat leaks into the system. From the refrigeration system 224 the oxygen line 222 passes through the non-reversing heat exchanger 2|9 into, a line 225. An oxygen line 226 having therein a valve 221 connects the main' oxygen line |66 with line 225.v This line 225 is provided with branches 226 and 229 leading into the oxygen flow paths |56 and |64, respectively. Flow path |6| is provided with an oxygen exit line 230.

7.-, In the operation of the modification of Figure |65, flow path |62, line |85, valve |80, line |81' into the air line 202. The air stream is thus cooled to a temperature near its condensation point and all carbon dioxide and moisture. if any, removed therefrom, the carbon dioxide being deposited in the flow paths |54 and |62 and the moisture, if any, in the flow paths |50 and |59. The air from line 202 flows through the heat exchanger 203 in heat exchange relation with oxygen passing through this exchanger, and also through exchanger 204 in heat exchange relation with the nitrogen passing through this exchanger and then into the high pressure column 200.

Nitrogen flows from the rectification system through line 2 |8 passing through heat exchangers 2|3, 206; 204, 2|9 into line |11. valvev |69, line |16, flow path |55, line |53, iiow path |5|, line |1|, valve |68 to the nitrogen exit line |14. Simultaneously, oxygen flows from the rectication system through line 220, heat exchanger 203, a portion of the oxygen stream depending upon the setting of valve 221 flowing through line 226 into line 225 and the remaining major portion flowing through line |88, valve |80, line |86, flow path |63, line |66, fiow path |60, line |82, valve |19 into and through the oxygen exit line |84. The portion of the oygen passing through line 226 flows through line 225 where it mixes with the recirculating oxygen, the oxygen mixture passing through the branch lines 228 and 229 into and through the oxygen ow paths |56 and |64 into the lines 22| and |61, respectively, both of which communicate with line 222. Part of the oxygen in line 222 is pumped by pump 223 through the refrigeration system 224, heat exchanger 2|9 and enters line 225 where it mixes as hereinabove described with the oxygen entering this line through line 226. The resultant oxygen stream is recirculated through the ow paths |56 and The remainder of the oxygen in line 222 flows through line |61, through the ow path |6| from which it is withdrawn through the oxygen exit line 230 as product uncontaminated by condensibles including carbon dioxide removed from the air stream.

Upon reversal, which may take place every three minutes, the air flows, in the case of the exchanger C, through valve |68, line |1|, flow path |5|, line |53, flow path |55, line |16. valve |69 into line |18 thence to line 202. In the case of exchanger D the air flow is through line |83, valve |19, line |82, flow path |60, line |66, flow path |63, line |86, valve |80, line |81, and thence to line 202 from which the flow is the same as hereinabove described in connection with the preceding step. Nitrogen flows from line |11 in to valve |69, line |15, ilow path |54. line |52, flow path |50, line |10, valve |68, thence through the nitrogen exit line |14. Oxygen flows through the recirculation system consisting of flow paths |56 and |64, lines 22| and |61, pump 229, refrigerating system 224, heat exchanger 2 |9, lines 225, 228 and 229, the same as hereinabove described. Also a portion of the oxygen to be withdrawn as product flows through flow path |6| as hereinabove described in connection with the preceding step of the process. In addition a major portion of the oxygen flowing through line 220 flows 16 through line |98 from which it flows through valve |80, line |85, flow path |62, line |65, flow path |59, line |8I, valve |19 into and through the oxygen exit line |84. The nitrogen, the flow of which is periodically reversed, in iiow paths |54, |55 in exchanger |49 and flow paths |50 and |5| in exchanger |49 and the oxygen, the flow of which is periodically reversed, in flow paths |62, |63 in exchanger |58 and |59 and |60 in exchanger |51 remove from their respective flow paths the carbon dioxide and other condensibles deposited therein from the air stream flowing therethrough during the preceding step of the.

process. The oxygen stream withdrawn as product flowing through flow path |6|, since it flows through a path'through which the air never passes, is uncontaminated by condensibles removed from the air stream.

One example of the operation of the process of this invention in the apparatus shown in Figure 1 is described below. It will be understood this example is given for purposes of exempliflcation only and the invention is not limited thereto. The example refers to an oxygen plant operating in a locality where the atmospheric pressure is 14.6 pounds per square inch absolute.

Air, which has not been pretreated to remove moisture and which is compressed to a pressure of about 89.5 pounds, is supplied at a temperature of F. through line 24, valve 22, line 26 to the flow path |2. The air leaves flow path |2 at a temperature of F. and proceeds through line I9. flow path |6, line 28, valve 23 and line 3|. The air leaves the flow path I6 at a temperature of 273 F.

Approximately 21% of the total air introduced into the process is expanded in expander 68. This fraction, which is to be expanded, flows through line 65 at a temperature of 273 F., entering and flowing through heat exchanger 62, the air being thus heated to a temperature of 239.5 F.; line 10 provides a by-pass around exchanger 62 through which part of the air may be passed to control the temperature of the air entering expander 68. Under normal operating conditions, by-pass 10 is closed. In expander 68 the air is expanded to a pressure of about 8.5 pounds, its temperature thus being reduced to 303 F., at which temperature and pressure it is introduced into the low pressure stage 36.

The remainder of the air (approximately 79%) at a temperature of 273 F. flows through line 3| into heat exchanger 5| in heat exchange relation with the nitrogen stream flowing through line 49 at a temperature of 294.5 F. and undergoes partial liquefaction (about 1% being liquefled) and passes at a temperature of 275 F. and a pressure of about 86 pounds into the high pressure stage 35 at12. The nitrogen owing through heat exchanger 5| is thus warmed to a temperature of 292 F.

The nitrogen stream at this temperature of 292 F. ows through line 54 and heat exchanger 53 leaving this exchanger at a temperature of about 281 F.; by-pass 55 is closed under normal operating conditions. The nitrogen stream at a temperature of about 281 F. passes through line 30, valve 23, line 29 into flow path |1 of heat exchanger section |0b. Thus the temperature differential between the entering nitrogen stream and the exiting air stream at the colder end of exchanger section |0b is 8 F. The nitrogen leaves ow path |1 at a temperature of 136 F. and passes through flow path I3, leav- 17 ing this ow path at a temperature of 80 F. and at substantially atmospheric pressure.

Oxygen at a temperature of 289 F. and a pressure of 8.8 pounds flows into line 32 where it mixes with the recirculated oxygen stream at a temperature of about 289 F. introduced into line 32 at 64. The mixed oxygen stream flows through path I5. About 38% of the oxygen which leaves path I at a temperature oi' 137.5 F. is returned by blower 60 through heat exchanger 62 where it is cooled to a temperature of about 218 F. and` then through heat exchanger 53 where it is cooled to a temperature of 289 F., at which temperature it mixes with the oxygen ilowing through line 32. The remainder of the oxygen flowing through line continues through flow path leaving this path at a temperature of 79.5 F. and at substantially atmospheric pressure. The stream exiting from line 33 contains approximately 96% by volume of oxygen.

In the operation of the rectification system 34, crude oxygen at a temperature of 275.5 F. and a pressure of about 86 pounds passes through line 42 through heat exchanger 43 in indirect heat exchange relation with nitrogen flowing through line 50. The crude oxygen is thus cooled to a temperature of 278 F. The crude oxygen is then flashed in its flow through expansion valve 45 entering section 36 as a vapor-liquid mixture at a temperature of about 306 F. and a pressure of about 8 pounds. Nitrogen at a temperature of 314 F. and a pressure of about 7 pounds flows through line into heat exchanger 40 where it is warmed to a temperature of 297 F. by indirect heat exchange with the nitrogen reux stream owing through line 39. The nitrogen at a temperature of 297 F. flows through exchanger 43 where it is warmed to a temperature of 294.5" F. at which temperature it enters exchanger 5| by way of line 49 in which it mixes with purge nitrogen owing through line 41. The nitrogen stream leaves exchanger 5| at a temperature of about 292 F., passes through exchanger 53 and flows into line 30at a temperature of 281 F.

Oxygen at a temperature of 289 F. and a pressure of 8.8 pounds ows through line 51 into line 32 wherein it mixes with the recirculating oxygen stream hereinabove described at a temperature at its point of mixing of 289 F. The resultant oxygen stream at a temperature of 289 F. as hereinabove described enters iiow path I5. For every 100 volumes of oxygen entering line 32 by way of line 51, about 62 volumes of recirculated oxygen are mixed therewith at the point 64 in line 32. This recirculation corresponds to about 13 volumes per 100 volumes of air entering the process, all volumes being measured under standard conditions.

Upon reversal, which may take place every three minutes. the air flows through paths |3 and I1, nitrogen through paths I6 and I2, and the oxygen continues to flow through paths I5 and The flow of the various streams is otherwise substantially the same as hereinabove described and the temperature and pressure conditions remain the same. The nitrogen in its flow through paths I6 and I2 removes by sublimation and evaporation the carbon dioxide and frost. if any, deposited in these paths by the air during the preceding step. Thus in the continued operation upon each reversal the nitrogen rectification product effects removal of the carbon dioxide and frost, if any, deposited in the paths 18 through which the air had passed during 'the preceding step of the process.

In the operation of the process of this invention it is preferred to effect removal of moisture and carbon dioxide both in accordance with the process of this invention. It will be understood, however, that if desired, the moisture may be removed from the air by any conventional means 4and dry air containing carbon dioxide passed through the exchanger or exchangers as hereinabove disclosed. In the event that dry air is supplied to the process and the exchanger system is similar to that of Figure 1, reversing valve 22 may advantageously be moved to the position between exchangers |0a and |0b, so that 'reversal of the air and nitrogen streams accurs only in exchanger Illb, wherein the carbon dioxide is deposited by the air stream. The reversing valves 68 and |19 of Figure 4 may be similarly positioned when the equipment of this figure is operated with dry air. Operating with dry air in equipment of the type shown in 1- igure 3 the reversing valves I4 and |25 may be placed at the warmer ends of regenerator sections 92, 95, 98 and I0|, and the regenerator sections 9| and 94, and 91 and |00 replaced with two non-reversing exchangers of the recuperative type. Operation of such arrangements is carried out so that the temperature at the warm end of exchangers |0b of Figure 1, 92, 95, 98 and |0| of Figure 3, |49 and |58 of Figure 4, is at least slightly higher than the temperature at which the carbon dioxide begins to deposit from the air stream. In general, the air entering the warm end of these exchangers should be at a temperature in the range of about to 160 F., the exiting product streams being about 10 to 15 F. colder.

As a desirable operating range the air is admitted to the inlet of the exchangers at a temperature of from 70 to 110 F. and a pressure of 60 to 100 pounds, preferably 75 to 90 pounds. The air in its ow through exchanger section Illa of Figure 1, |48 and |51 of Figure 4, or regenerator sections 9|, 94, 91 and |00 of Figure 3, is cooled to a temperature of about 110 to 160 F. and at this temperature enters, respectlvely, exchanger section I0b of Figure 1, |49 and |58 of Figure 4, or regenerator sections 92, 95, 98 and |0| of Figure 3, exiting therefrom at a temperature within the range of 260 to 280 F. In general the oxygen rectification product enters the exchangers at a temperature of from 288 to 293 F., the nitrogen enters at a temperature of from 265 to 285 F., and both the oxygen and nitrogen leave the exchangers at a temperature of from 60 to 100 F. In the modifications involving split or srctional exchangers, e. g., the modifications of Figures 1, 3 and 4, the oxygen leaves exchanger |0b of Figure l, nitrogen leaves regenerator sections 98 and IIJI of Figure 3 and oxygen leaves the exchanger sections |49 and |58 of Figure 4 at a temperature of from about to 175 F. and the nitrogen leaves exchanger |0b of Figure 1, regenerator section 92 or 95 of Figure 3 and exchanger section |49 of Figure 4 at a temperature of from about 120 to 175 F. The high pressure stage of the rectication system is maintained at about 60 to 100 pounds and the low pressure stage at about 5 to 12 pounds. The several streams suffer only a small pressure drop in flowing through the exchangers.

It is generally advisable to recirculate a volume of gasous rectication product through at least the colder end oi' the exchangers corresponding to from about 10% to `about 25% of the volume -ot the air entering the process. all v'olumes bea rectification product stream instrumental inimproving the emciency of the purging is withdrawn as product uncontaminated by condensibles removed from the air.

The expressions "reversing the now ot air and nitrogen or of air and oxygen" and "reversal are used herein in the sense commonly employed in this art, namely, to mean the switching of the flow of two streams, for example, the air and the nitrogen or oxygen streams, so that upon each reversal" the air flows through the path through which had previously flowed the nitrogen or oxygen and the nitrogen or oxygen flows through the path through which had previously flowed the air. The term "path" is used herein in a comprehensive sense to include the flow arrangement of Figure 3 in which the non-reversing recirculating nitrogen stream flows through a path consisting oi' four sections in parallel as well as paths consisting of sections in series as shown. for example. in Figure 1.

Since certain changes may be made in carry- -lng out the4 above processes without departing from the scope of the invention, it is intended that all matter containedin the above description shall be interpreted as illustrative and not in a limiting sense. Th-us, for example, instead of recirculating oxygen or nitrogen rectification products, other rectification products such as argon, neon, krypton or welding grade oxygen, may be recirculated through at least the cold end of the exchangers and the recirculated stream oi' such additional rectification product employed to improve the purging and still permit the withdrawal of the additional rectification product uncontaminated with condensibles removed from the air. This application contains claimsY generic to such operation; my copending application Serial No. 783,552 led Novem-ber 1. 1947, now Patent No. 2,513,306 of July 4, 1950, discloses and claims the modification involving the recirculation of an additional rectification product stream.

Whatis claimed is:

1. A process for producing oxygen by the liqueiaction and rectification of air, which comprises passing a stream of rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange zone, cooling the air to a temperature close to its condensation point at the pressure prevailing in the air flow path in said heat exchange zone and eilecting substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone. subjecting the thus cooled air to rectification t produce said rectification product stream, periodically reversing the flow of the air stream and the said rectification product stream through their respective flow paths in said zone. passing a second stream of rectification product through rits entry into said heat exchange zone, thereby l a path extending through at least the colder end of said. heat exchange zone in heat exchange relation with the air and the first-mentioned -stream Bof rectincation product passing therethrough, recirculating a portion of said second stream oi' rectification product leaving said lastmentioned path through said last-mentioned path. and withdrawing a portion of the recirculated stream of rectification product as product uncontaminated by carbon dioxide .Y removed from the air stream.

2. The process of claim 1 mentioned stream of rectification product is predominantly nitrogen and the second stream ot rectincation product is predominantly oxygen.

3,. A process for producing oxygen by the liqueiaction andvrectification of air in a rectification system involving high and low pressurelstages. which comprises passing a stream of rectiilcation product through a path in a heat exchange zone, passing a stream' of air through another path in said heat exchange zone, cooling the air to a temperature close to its condensation point at the pressure prevailing in the air flow path in -said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, dividing the air stream into major and minor portions, passing the major portion to the high pressure stage of the rectification system, passing a second stream of rectification product through at least the colder end of said heat exchange zone in indirect heat exchange relation with the air and said first-mentioned rectincation product stream, thereby warming said second stream'oi' rectification product, passing the thus warmed stream of rectification product in indirect heat exchange relation with (l) at least a part of said minor portion of the air stream, thereby warming said minor portion to a temperature such that said minor portion can thereafter be expanded without substantial liquefaction, and (2) at least a portion of the rstmentioned rectification product stream prior to warming said rectiiication product stream to a temperature within 5 to 10 F. of the temperature of the air stream leaving said heat exchange une', expanding said warmed minor portion of the air to produce refrigeration in amount sufiicient to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the process and introducing the expanded air into the low pressure stage of the rectification system, and periodically reversing the ilows of the air and the mst-mentioned rectification product stream through their respective paths in said zone. whereby upon each of said reversals the firstmentioned stream of rectification product substantially completely removes the carbon dioxide deposited in said zone during the preceding step of the process.

4. A process for producing oxygen by the liquefaction and rectification of air in a 'rectification system involving a high pressure stage maintained at a pressure of to 100 pounds and a low pressure stage maintained at a pressure of from 5 'to 12 pounds, which comprises passing a stream vof rectification product from the low pressure wherein the nrstdensation point at the pressure prevailing in said air flow path in said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through its flow path, introducing the thus cooled air to thev high pressure stage of said rectification system, periodically reversing the flows of the air and the said rectification product through their respective paths in said zone, passing a second stream of rectification product from the rectification system through a path extending through at least the colder end of said heat exchange zone in indirect heat exchange relation with the air stream and the first-mentioned rectification product stream passing therethrough. recirculating .a portion of said second stream of rectification product leaving said last-mentioned path through said last-mentioned path, and withdrawing a portion of the recirculated stream of rectification product as product uncontaminated by carbon dioxide removed from the air stream.

5. A process for producing oxygen by the liquefaction and rectification of air in a rectification system involving a high pressure stage maintained at a pressure of from 60 to 100 pounds and a low pressure stage maintained at a pressure of from to 12 pounds, which comprises passin': a stream of nitrogen rectification product from the low pressure stage through a path in a heat exchange zone and passing a stream of air at a pressure of from to 100 pounds at a temperature of from to 110 F. into and through another path in said heat exchange zone, cooling the air to a temperature close to its condensation point at the pressure prevailing in its flow path through said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, dividing the air stream into major and minor portions, passing the major portion to the high pressure stage of the rectification system, passing a stream of oxygen rectification product from the low pressure stage through a path extending through at least the colder end of said heat exchange zone in indirect heat exchange relation with the air and nitrogen rectification product stream passing there.

through, thereby warming said oxygen rectification product stream, passing the thus warmed oxygen rectification product stream in indirect heat exchange relation with (l) at least a part of said minor portion of the air stream thereby Warming said minor portion to a temperature such that said minor portion can thereafter be expanded Without substantial liquefaction, and (2) at least a part of the nitrogen rectification product stream prior to its entry into said heat exchange zone, thereby warming said nitrogen stream to a temperature within 5 to 10 F. of the temperature of the air stream leaving said heat exchange zone, expanding said warmed minor portion of the air to produce refrigeration in amount sufficient to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the process, introducing the expanded air into said low'pressure stage, periodically reversing the flows of the air and the said nitrogen rectification product stream through their respective paths in said zone, whereby upon each of said reversals the nitrogen rectification product 22 stream substantially completely removes the carbon dioxide deposited in said zone during the preceding step of the process, and withdrawing a portion of the said oxygen rectification product stream as product uncontaminated by condensibles removed from the air stream.

6. The process for producing oxygen by the liquefaction and rectification of air, which coniprises passing a, stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange Vzone countercurrent to the direction of flow of said nitrogen stream, cooling the air to a, temperature close to its condensation point at the pressure prevailing in its fiow path through said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, periodically reversing the flows of the air and nitrogen rectification product streams through their respective paths in said zone, introducing the thus cooled air into a rectification system, passing a second stream of rectification product through a path in said heat exchange zone in a direction cocurrent with the flow of said nitrogen stream and countercurrent to the flow of said air stream, at a point in the flow of said second stream of rectification product where its temperature is within the range of to 175 F., withdrawing a portion of said second stream ofrectification product and recirculating the portion thus withdrawn vthrough the path through which the second stream of rectification product flows through said heat exchange zone, and removing the remainder of said Second stream of rectification product from the exit end of its flow path as product uncontaminated by condensibles removed from the air stream.

"7. The process for producing oxygen by the liquefaction and rectification of air, which comprises passing a. stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange zone countercurrent to the direction of flow of said nitrogen stream, cooling the air to a tempearture close to its condensation point at the pressure prevailing in its flow path through said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, periodically reversing the flows of the air and nitrogen rectification product streams through their respective paths in said zone, introducing the thus cooled air into a rectification system, passing a stream of oxygen rectitication product through a path in said heat exchange zone in a direction cocurrent with the flow of said nitrogen stream and countercurrent to the flow of said air stream, at a point in said oxygen iiow stream path where the temperature of the oxygen is within the range of 120 to F. withdrawing a portion of the oxygen, recirculating the portion of oxygen thus Withdrawn through the same path through which the oxygen rectification product stream has passed in said heat exchange zone, and removing the remainder of the oxygen rectification product stream from the exit end of its now path as product uncontaminated by condensibles removed from the air stream.

8. The process for producing oxygen by the liquefaction and rectification of air in a rectification system involving high and low pressure stages, which comprises passing a stream of nitrogen rectiiication product through a path in prevailing in its iiow path through said heat exchange zone and eiiecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, dividing the air stream into major and minor portions, passing the major portion to the high pressure "stage ot the rectincation system, a second stream of rectification product through a path extending through at least the colder end of said heat exchange none in indirect heat exchange relation with the alr and said first-mentioned rectincation product stream, thereby warming said second stream o! rectification product at a point in the iiow of the second stream of rectiiication product where its temperature is within the range of 120 to 175 F., withdrawing a portion of the second rectiiication product and recirculating the portion thus withdrawn through the said path through which the second rectification product stream ows through said heat exchange zone, removing the remainder of the second rectification product stream from the exit end of its ilow path as product uncontaminated by condensibles removed from the air stream, passing the recirculated portion of the said second stream of rectincation product in indirect heat exchange relation with (1) at least a part of said minor portion of the air stream, thereby warming said minor portion to a temperature such that said minor portion 'can thereafter be expanded without substantial liqueiaction and (2) at least a part of the first-mentioned rectification product stream prior to its entry into said heat vexchange zone, thereby warming said rectiiication product stream to a temperature within 5 to 10 F. of the temperature oi the air stream leaving said heat exchange zone. expanding said warmed minor portion of the air to produce refrigeration in amount sufficient to compensate for cold losses resulting from the difierence in enthalpy between the incoming air and the outgoing products o! rectification and for heat leaks into the process, introducing the expanded air into the low pressure stage of the rectiflcation system, and periodically reversing the flows of the air and nitrogen rectiiication product streams through their respective paths in said zone.

9. The process for producing oxygen by the liquefaction and rectication of air in a rectiilcation system involving a high pressure stage maintained at a pressure of from 60 to 100 pounds and a low pressure stage maintained at a pressure of from 5 to 12 pounds, which comprises passing a stream of nitrogen rectiilcation product from the low pressure stage through a path in a heat exchange zone, passing a stream of air at a pressure of from 60 to 100 pounds at a temperature of from 70 to 110 F. through another path in said heat exchange zone countercurrent to the direction of fiowoi said nitrogen stream. cooling the air to a temperature close to its condensation point at the pressure prevailing in its ilow path through said heat exchange zone and effecting the substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zone, dividing the air stream into major and minor portions, passing the major portion to the high pressure stage of the rectiiication system, passing a stream of oxygen rectication product from the said low pressure stage through a path extending through at least the colder end of said heat exchange zone in indirect heat exchange relation with the air and said nitrogen rectiiication product stream, thereby warming said oxygen stream of rectification product at a n point in said oxygen flow stream path where the temperature of the oxygen is within the range of to 175 F., withdrawing a portion of the oxygen and recirculating the portion thus withdrawn through the said path through which the oxygen rectification product stream flows through said heat exchange zone, removing the remainder of the oxygen rectiiication product stream from the exit end of its iiow path as product uncontaminated by condensibles removed from the air stream, passing the recirculated portion of said stream of oxygen in indirect heat exchange relation with (l) at least a part of said minor portion of the air stream, thereby warming said minor portion to a temperature such that said minor portion can thereafter be expanded without substantial liquefacton and (2) at least a part of the nitrogen rectication product stream l prior to its entry into said heat exchange zone, thereby warming said nitrogen rectification product stream to a temperature within 5 to 10 F. of the temperature of the air stream leaving said heat exchange zone, expanding said warmed minor portion of the air to a pressure of from 5 to 12 pounds, thereby producing refrigeration in amount suiiicient to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectitication and i'or heat leaks into the process, introducing the expanded air into the low pressure stage of the rectiiication system, and periodically reversing the ilows of the air and nitrogen rectiilcation product streams through their respective paths in said zone.

l0. A process for producing oxygen by the liqueiaction and rectification ofair, which comprises passing a stream of rectiiication product through one of a pair of regenerators while simultaneously passing through the other of said regenerators a stream of air, periodically reversing the iiow of said air stream and rectification product stream through the regenerators of said pair, whereby said air stream recovers the cold content of the rectiiication product stream, is cooled to a temperature close to its condensation point at the pressure prevailing in its flow through said regenerator, carbon dioxide is substantially completely removed from the air stream in its ow through said regenerators and the rectification product stream substantially completely removes the carbon dioxide deposited in the regenerator through which the air flows during the preceding step of the process, introducing the thus cooled air into the rectication system, passing a second stream of rectification product through at least the cold ends of said regenerators in indirect heat exchange relation with the gaseous media passing therethrough, withdrawing a portion of the second-mentioned stream of rectification product as product uncontaminated by condensibles removed irom the air stream, and recirculating the remainder of said second stream of rectification product through its ow path in said regenerators.

l1. A process for producing oxygen by the liquefaction and rectification oi air, which comprises passing a stream oi' nitrogen rectication product through one of a pair of regenerators while simultaneously passing through the other of said regenerators a stream of air, periodically reversing the fiow of said air stream andnitrogen rectification product stream through the regenerators of said pair whereby the air stream recovers the cold content of the nitrogen rectification product stream, is cooled to a temperature close to its condensation point at the pressure prevailing in its fiow through said regenerator, carbon dioxide is substantially completely removed from said air stream in its fiow through said regenerators and the nitrogen rectification product stream substantially completely removes the carbon dioxide deposited in the regenerator through which the air hows/during the preceding step of the process, introducing the thus cooled air into the rectification system, passing a stream of oxygen rectification product through at least the cold ends of said regenerators in indirect heat exchange rela tion with the nitrogen and air passing therethrough, the oxygen fiowing cocurrently with the nitrogen stream and countercurrent to the direction of flow of the air stream, withdrawing a portion of the oxygen stream as product uncontaminated by condensibles removed from the air stream, and recirculating the remainder of the oxygen stream through its fiow path in at least the cold ends of said regenerators.

12. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectification product through one of a pair of' regenerators while simultaneously passing through the other of said regenerators a stream of air, periodically reversing the fiow of said air stream and nitrogen rectification product stream through the regenerators of said pair whereby the air stream recovers the cold content of the nitrogen rectification product stream, is cooled to a temperature close to its condensation point at the pressure pre vailing in its flow through said regenerator, carbon dioxide is substantially completely removed from said air stream in its fiow through said regenerators and the nitrogen rectification product stream substantially completely removes the carbon dioxide deposited in the regenerator through which the air fiows during the preceding step of the process, introducing the thus cooled air into the rectification systempassing a stream of oxygen rectification product through said regenerators in indirect heat exchange relation with the nitrogen and air passing therethrough, withdrawl ing a portion of the oxygen stream as product uncontaminated by condensibles removed from the air stream, and recirculating the remainder of the oxygen stream through its fiow path in said regenerators.

13. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectification product through one of a pair of regenerators While simultaneously passing a stream of air through the other of said regenerators, passing a stream of oxygen rectification product through one of a second pair of regenerators while simultaneously passing air through the other of said pair of regenerators, periodically reversing the fiow of nitrogen `and air through the respective regenerators of the first-mentioned pair and the fiow of oxygen and air through the respective regenerators of the second-mentioned pair, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing in its fiow through said regenerators, effecting the substantially complete removal of carbon dioxide from the air in its passage through said regenerators, and effecting substantially complete removal of the carbon dioxide deposited in the regenerators, and recirculating a stream of rectification product through at least the colder ends of all of said regenerators in indirect heat exchange relation with the gaseous media passing therethrough.

14. A process for producing oxygen by the liquefaction and rectification of' air, which comprises passinga stream of nitrogen rectification product through one of a pair of regenerators while simultaneously passing a stream of air through the other of said regenerators, passing a stream of oxygen rectification product through one of a second pair of regenerators while simultaneously passing air through the other of'said pair of regenerators, periodically reversing the` flow of nitrogen and air through the respective regenerators of the first-mentioned pair and the fiow of oxygen and airthrough the respective regenerators of the second-mentioned pair, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing in its fiow paths in said regenerators through which the air flows, effecting the substantially complete removal of carbon dioxide from the air in its passage through said regenerators and effecting substantially complete removal of the carbon dioxide deposited in the regenerators, recirculating a stream of nitrogen rectification product through at least the colder ends of all of said regenerators in indirect heat exchange relation with the gaseous media passing therethrough, and withdrawing a portion of the recirculating stream of nitrogen rectification product uncontaminated by condensibles removed from the air stream.

15. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectification product through one of a pair of regenerators while simultaneously passing a stream of air through the other of said regenerators, recirculating a stream of oxygen rectification product throughat least the colder ends of said pair of regenerators in indirect heat exchange relation with the gaseous media passing therethrough, periodically reversing the fiow of nitrogen and air through their respective regenerators, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing in its fiow paths through said regenerators when the air flows therethrough, effecting the substantially complete removal of carbon dioxide from the air in its passage through said regenerators and effecting substantially complete removal of the carbon dioxide deposited in the regenerators by the nitrogen rectification product stream passing therethrough, and withdrawing a portion of the recirculating oxygen stream uncontaminated by condensibles removed from the air stream.

16. A process for producing oxygen by the liquefaction and rectification of air, which cornprises passing a stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange zone to recover the cold content of the nitrogen rectification product stream, cooling the air to a temperature close to its condensation point at the pressure prevailing in the air flow path in said heat exchange zone and effecting substantially complete removal of carbon dioxide from the air in its passage through 27 said heat excha'nge zone, passing a stream of oxygen rectification product through a path in .a second heat exchange zone, passing a stream of air through another path in said second heat exchange zone to recover the cold content of the oxygen rectification product stream, cooling the air to a temperature close to its condensation point at the pressure prevailing in the air fiow path in said second heat exchange zone and effecting substantially complete removal of carbon dioxide from the air in its passage through said second heat exchange zone, passing a second stream of oxygen rectification product in two parts, respectively, through a unidirectional fiow path in at least the colder -end of the first-mentioned heat exchange zone and a unidirectional iow path in at least the colder end of said second heat exchange zone, thus warming said second oxygen stream, passing the thus warmed second oxygen stream in indirect heat exchange relation with the stream of nitrogen supplied to the first-mentioned heat exchange zone, thereby cooling said warmed second oxygen stream, recirculating the thus cooled second oxygen stream in two parts, respectively, through said unidirectional flow paths, periodically reversing the fiow of air and nitrogen through their respective paths in the first-mentioned heat exchange zone and the iiow of air and oxygen through their respective paths in said second heat exchange zone, and withdrawing a portion of said second oxygen stream as product uncontaminated by condensibles removed from the air streams.

17. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a first stream of rectification product through a path in each of two heat exchange zones arranged in parallel, passing a second stream of air through another path in each of said two heat exchange zones, thereby cooling the air to a temperature close to its condensation point at the pressure prevailing in the air flow paths in said two heat exchange zones and effecting substantially complete removal of carbon dioxide from the air in its passage through said two heat exchange' zones, passing a third stream of rectification product through a unidirectional ow path in at least the colder end of each of said two heat exchange zones, thus warming said third stream of rectification product, recirculating a portion of the warmed third stream of rectification product through said unidirectional flow path of at least one of said two heat exchange zones, periodically reversing the flow of air and said first stream of rectification product throughv their respective paths in each of said two heat exchange zones, and withdrawing a portion of the warmed third stream of rectification product as product uncontaminated by carbon dioxide re- 28 moved from the air in said two heat exchange zones. 4

18. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a first stream of rectification product through a path in each of two heat exchange zones arranged in parallel, passing a second stream of air through another path in each of said two heat exchange zones, thereby cooling the air to a temperature close to its condensation point at the pressure prevailing in the air flow paths in said two heat exchange zones and effecting substantially complete removal of carbon dioxide from the air in its passage through said two heat exchange zones, passing a third stream of rectification product through a unidirectional flow path in at least the colder end of each of said two heat exchange zones, thus warming said third stream of rectification product, cooling a portion of the warmed third stream of rectifica tion product, recirculating the cooled portion through said unidirectional iiow path of at least one of said two heat exchange zones, periodically reversing the fiow of air and said first stream of rectification product through their respective paths in each of said two heat exchange zones, and withdrawing a portion of the warmed third stream of rectiiication product as product uncontaminated by carbon dioxide removed from the air in said two heat exchange zones.

19. The process of claim 18 wherein the cooling of a portion of the warmed third stream of rectiiication product is effected by passing said warmed portion in heat exchange relation with the first stream of rectification product flowing to one of said two heat exchange zones.

PAUL W. GARBO.

REFERENCES CITED The following references vare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,433,604 Dennis Dec. 30, 1947 2,460,859 Trumpler Feb. 8, 1949 FOREIGN PATENTS Number Country Date 276,381 Great Britain Aug. 18, 1927 OTHER REFERENCES Refrigerating Engineer, January 1947, page 24, Low Pressure Liquefaction of Air, by J. Henry Rushton.

Transactions American Institute Chemical Engineers, February 1947, volume 43, No. 2, page 69; Air Purification in the Reversing Exchanger, by W. E. Lobo and G. T. Skaperdos. 

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING A STREAM OF RECTIFICATION PRODUCT THROUGH A PATH IN A HEAT EXCHANGE ZONE, PASSING A STREAM OF AIR THROUGH ANOTHER PATH IN SAID HEAT EXCHANGE ZONE, COOLING THE AIR TO A TEMPERATURE CLOSE TO ITS CONDENSATION POINT AT THE PRESSURE PREVAILING IN THE AIR FLOW PATH IN SAID HEAT EXCHANGE ZONE AND EFFECTING SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE AIR IN ITS PASSAGE THROUGH SAID HEAT EXCHANGE ZONE, SUBJECTING THE THUS COOLED AIR TO RECTIFICATION TO PRODUCE SAID RECTIFICATION PRODUCT STREAM, PERIODICALLY REVERSING THE FLOW OF THE AIR STREAM AND THE SAID RECTIFICATION PRODUCT STREAM THROUGH THEIR RESPECTIVE FLOW PATHS IN SAID ZONE, PASSING A SECOND STREAM OF RECTIFICATION PRODUCT THROUGH A PATH EXTENDING THROUGH AT LEAST THE COLDER END OF SAID HEAT EXCHANGE ZONE IN HEAT EXCHANGE RELATION WITH THE AIR AND THE FIRST-MENTIONED STREAM OF RECTIFICATION PRODUCT PASSING THERETHROUGH, RECIRCULATING A PORTION OF SAID SECOND STREAM OF RECTIFICATION PRODUCT LEAVING SAID LASTMENTIONED PATH THROUGH SAID LAST-MENTIONED PATH, AND WITHDRAWING A PORTION OF THE RECIRCULATED STREAM OF RECTIFICATION PRODUCT AS PRODUCT UNCONTAMINATED BY CARBON DIOXIDE REMOVED FROM THE AIR STREAM. 